1. Field of the Invention
The invention relates to tunable embedded inductor devices, and in particular to tunable embedded high frequency integrated inductor devices.
2. Description of the Related Art
Embedded inductor devices have been applied in various circuits including resonators, filters, and matching networks. Among applications of wireless communication, digital computer, portable electronics, and information household appliance, features with higher frequencies, broader bandwidths, and miniaturization have become main requirements of high-tech industries and commercial markets. During development and design of high frequency circuit modules, consideration must be given to inductor devices, as they are electrically coupled to other peripheral circuits or devices and may be vulnerably interfered with thereof. Additionally, the inductor devices can be affected by process and material variations such that characteristics of the inductor devices are not precise, resulting in detrimental performance of the entire circuitry. For example, when an inductor device is configured in an oscillator, oscillation frequency of the oscillator can be shifted due to inductance deviation of the inductor device. Therefore, a tunable embedded inductor device is needed to meet specifications of oscillators.
When conventional embedded inductor devices, such as spiral inductors or solenoid inductors are applied in a circuit module, inductance of the embedded inductor devices is regulated by changing circuit layout design. Each time the circuit layout design is changed, the high frequency circuit module testing boards are also remade, thereby increasing processing period and fabrication costs.
U.S. Pat. No. 6,005,467, the entirety of which is hereby incorporated by reference, discloses a three dimensional wound inductor device. An additional electric conductive shorting member extending and electrically connected between windings is introduced during the inductor winding process to adjust inductance of the entire circuit.
FIG. 1 is a stereographic view of a conventional three dimensional wound inductor device. Referring to FIG. 1, a three dimensional (3D) wound inductor device 1 includes a substrate 20 and two lateral planes 10 and 12. Three turns of windings 22, 24, and 26 surround the substrate 20 configured as a solenoid coil. An electric conductive shorting member 28 is disposed on one of the lateral planes connecting each turns of windings 22, 24, and 26 at wielding spots 32, 34 and 36. By cutting the electric conductive shorting member 28 at cutting site C, inductance of the 3D wound inductor device 1 is adjusted as winding turns of the solenoid coil change. However, formation of the electric conductive shorting member is not suitable for regulating high frequency inductor device embedded in functional substrates.
Furthermore, U.S. Pat. No. 6,727,571, the entirety of which is hereby incorporated by reference discloses a tunable embedded inductor device. Inductance of the inductor device can be adjusted by trimming width of the conductive windings. FIG. 2 is a schematic view of a conventional planar wound inductor device. Referring to FIG. 2, a planar wound inductor device includes a planar spiral coil 52 disposed on a substrate 51. The planar spiral coil 52 is composed of segments 52a, 52b, 52c, and 52d arranged as a loop. By trimming the width of the segments 52a, 52b, 52c, and 52d and by changing interval therebetween, inductance of the planar wound inductor device can be regulated. Conventional planar wound inductor devices can not be integrated into multi-layered inductor structures. More specifically, when a passivation layer or an outer substrate is formed on the planar wound inductor device, it is difficult to precisely trim segments of the planar spiral coil.